BERLIN - German doctors treating Pyotr Verzilov, a member of Russian protest group Pussy Riot, said Tuesday that claims he was poisoned are "highly plausible" but stressed they can't say how this might have occurred or who was responsible.

Dr. Kai-Uwe Eckardt of Berlin's Charite hospital told reporters that Verzilov has been receiving intensive care since arriving in Berlin from Moscow on Saturday, but his condition isn't life threatening.

Verzilov's symptoms, together with information received from relatives and the Moscow hospital he was admitted to last week, "make it highly plausible that a poisoning took place," Eckardt said. He said Charite doctors have found "no evidence whatsoever that there would be another explanation for his condition."

Verzilov and other members of the Pussy Riot group served 15-day jail sentences for disrupting July's World Cup final to protest excessive Russian police powers.

Eckardt said Verzilov fell ill on Sept. 11 after attending a friend's court hearing in the Russian capital, and was admitted to a Moscow hospital that evening with symptoms that included disorientation and widened pupils. Russian doctors suspected possible poisoning and treated him accordingly, emptying his stomach and performing a dialysis, said Eckardt.

He said the symptoms indicate Verzilov, who arrived in Germany by private medevac Saturday, is suffering from an anticholinergic syndrome that can result from the disruption of the nervous system that regulates the inner organs.

While doctors in Berlin haven't yet determined what was responsible for the poisoning, they said it could have resulted from various substances including high doses of some pharmaceuticals and plants that contain particular toxins.

Dr. Karl Max Einhaeupl, the Charite hospital's chairman, said doctors wanted to "refrain completely from all speculation about what made these problems happen."

While he wouldn't rule out that recreational drugs were responsible for the poisoning, he said such drug use is very rare.

"We have no evidence that there is a drug problem and it would be very unusual for someone to take a drug in the dose that it was taken," he said. "That would be done with suicidal intent, but we have no indications of this."

Eckardt, who heads the Charite's intensive care department, said he expects Verzilov to make a full recovery and hopefully suffer no permanent damage.

He said Verzilov, who also has Canadian citizenship, is already communicating with doctors but so far they haven't been able to question him in detail about his medical history.

A fellow member of Pussy Riot, Nadezhda Tolokonnikova, told reporters at a separate news conference in Berlin on Tuesday that Verzilov was "one of the most effective activists that Russia has ever seen."